aictx: Performance improvments to handle duplicates, gitignore awareness, integration tests, and new flags

[Unique-Divine]

• mdtoc: Fix indentation when firsth1: false: recalculate highest after removing the first H1 so top-level headings (e.g., H2) start at level 0
• aictx: Fix path-dedup logic by keying on absolute paths and switching RunCtx to pointer receivers.
• aictx: Write tests for function that finds the git repo path
• aictx: Go deps
• aictx: Impl git ignore utils to begin work on integrating ignore files into the tool.
• aictx: Add gitignore loading, ignore evaluation
• aictx: tests for git ignore behavior during runs and skip dir semantics
• aictx: impl depthWithinRoot function to use --level flag
• aictx: impl --level flag behavior for max recursion depth from each root path
• aictx: impl tests for new --level flag
• aictx: Refactor project to run main.go into a thin wrapper, making it easier to write integration tests that use the full CLI
• aictx: Route CLI output through cli.App writers instead of os.Stdout/os.Stderr for testability.
• aictx: Add CLI-level integration tests and a test harness for capturing stdout/stderr.
• aictx(deps): Update urfave/cli to v3; cleaner file header for each output in the buffer
• aictx: Add justfile with commands for tests, linting, formatting, and building the app
• docs: Update README.md to to reflect updates to algos and aictx dirs
• aictx: Add a README.md file with examples
• aictx: split ignore logic into global and local layers
• chore: update LICENSE